An electric vehicle requires a power source having a large capacity and hence, a battery module which includes a plurality of battery cells is used.
A battery module of this type includes: a plurality of battery cells arranged in a row in one direction; a plurality of spacers each of which is arranged between every two battery cells arranged adjacently to each other in the one direction; and a pair of spacers for end portions which is arranged on outer sides of the plurality of battery cells in the one direction (see JP-A-2014-36001, for example).
The battery module is also configured such that the respective battery cells are cooled by allowing a cooling medium to flow through gaps formed between the respective battery cells. In the battery module of this type, each spacer has cutaway portions formed over the whole length in the width direction of the battery cell. Accordingly, in the battery module of this type, each battery cell is supposed to be cooled by allowing a cooling medium to pass through the inside of the cutaway portion of each spacer.
In such a battery module, the cutaway portions of the respective spacers are formed uniformly. Accordingly, in the battery module, there may be a case where the temperature of a cooling medium which passes through the inside of the cutaway portions of the spacers becomes irregular among the respective spacers. In such a case, in the respective battery cells, a heat exchange is performed with cooling mediums having different temperatures. Accordingly, in the battery module, there may be a case where the temperatures of the respective battery cells become irregular.
For example, the battery module may be used in such a manner that a cooling medium is supplied to the battery module from a supply device arranged around one end portion of the battery module in one direction, and the cooling medium is discharged from a discharge device arranged around the other end portion of the battery module in the one direction.
In the case where the temperature of the supply device or the temperature of the discharge device is increased, heat generated by the supply device is transferred to a cooling medium which flows around the one end portion of the battery module, and heat generated by the discharge device is transferred to a cooling medium around the other end portion of the battery module. Accordingly, the temperature of a cooling medium which passes through the inside of the respective cutaway portions of the pair of spaces for end portions of the battery module becomes higher than the temperature of a cooling medium which passes through the inside of the cutaway portions of the plurality of spacers each of which is arranged between every two battery cells arranged adjacently to each other in the one direction.
That is, the temperature of the cooling medium which cools the respective battery cells arranged at both ends of the battery module in the first direction among the plurality of battery cells becomes higher than the temperature of the cooling medium which cools the respective battery cells arranged between both ends of the battery module in the first direction among the plurality of battery cells.
Accordingly, in the battery module, among the plurality of battery cells, there may be a case where the temperatures of the respective battery cells arranged at both ends of the battery module in one direction become higher than the temperature of other battery cells so that the temperatures of the respective energy storage devices become irregular.